BUG#934597: Assertion `! is_set()' failed in Diagnostics_area::set_ok_status(THD...

- After the exec_const_cond->val_int() call, check for error and return.
  (if we don't do it, we will eventually hit an error when trying to set status OK in 
   the diagnostics area, which already has an error status).

mysql-test/r/subselect4.result

@@ -2141,6 +2141,20 @@ WHERE t2.b IN (SELECT t3.b FROM t3 WHERE t3.a < ANY (SELECT t4.a FROM t4) and t3
 c	a	b
 10	7	0
 drop table t2, t3, t4;
+#
+# BUG#934597: Assertion `! is_set()' failed in Diagnostics_area::set_ok_status(THD...
+#
+CREATE TABLE t1 ( a VARCHAR(1) );
+INSERT INTO t1 VALUES ('u'),('k');
+CREATE TABLE t2 AS
+SELECT a AS field1 FROM t1
+WHERE ( SELECT alias1.a
+FROM t1 AS alias1
+) IS NOT NULL;
+ERROR 21000: Subquery returns more than 1 row
+DROP TABLE t2;
+ERROR 42S02: Unknown table 't2'
+DROP TABLE t1;
 set optimizer_switch=@subselect4_tmp;
 SET optimizer_switch= @@global.optimizer_switch;
 set @@tmp_table_size= @@global.tmp_table_size;

mysql-test/t/subselect4.test

@@ -1779,6 +1779,22 @@ WHERE t2.b IN (SELECT t3.b FROM t3 WHERE t3.a < ANY (SELECT t4.a FROM t4) and t3
 
 drop table t2, t3, t4;
 
+--echo #
+--echo # BUG#934597: Assertion `! is_set()' failed in Diagnostics_area::set_ok_status(THD...
+--echo #
+CREATE TABLE t1 ( a VARCHAR(1) );
+INSERT INTO t1 VALUES ('u'),('k');
+--error ER_SUBQUERY_NO_1_ROW
+CREATE TABLE t2 AS
+ SELECT a AS field1 FROM t1
+ WHERE ( SELECT alias1.a
+         FROM t1 AS alias1
+       ) IS NOT NULL;
+--error ER_BAD_TABLE_ERROR
+DROP TABLE t2;
+DROP TABLE t1;
+
+
 set optimizer_switch=@subselect4_tmp;
 
 SET optimizer_switch= @@global.optimizer_switch;

sql/sql_select.cc

@@ -2161,6 +2161,15 @@ JOIN::exec()
       !exec_const_cond->val_int())
     zero_result_cause= "Impossible WHERE noticed after reading const tables";
 
+  /* 
+    We've called exec_const_cond->val_int(). This may have caused an error.
+  */
+  if (thd->is_error())
+  {
+    error= thd->is_error();
+    DBUG_VOID_RETURN;
+  }
+
   if (zero_result_cause)
   {
     (void) return_zero_rows(this, result, select_lex->leaf_tables,